The ESBWR an advanced Passive LWR

Transcription

1 1 IAEA PC-Based Simulators Workshop Politecnico di Milano, 3-14 October 2011 The ES an advanced Passive LWR Prof. George Yadigaroglu, em. ETH-Zurich and ASCOMP

2 2 Removal of decay heat from evolutionary LWRs with active systems Assured by redundant and diverse active ECCS and containment cooling systems High degrees of reliability and safety can be achieved by increasing system redundancy, separation, diversity, etc. Such improvements may bring, however, added complexity and costs to the systems

3 3 Advanced passive ALWR designs - 1 Replacement of active emergency core and containment cooling systems with passive ones: no active components such as pumps, fans, diesels, water chillers, etc. Simple re-alignment of valves allowed Use only natural devices or forces such as gravity, natural circulation, passive heat sink, stored energy (e.g. compressed gas) to operate Passive heat sinks: Containment structures, water pools or the atmosphere

4 4 Advanced passive LWR designs - 2 Require no operator actions to mitigate DBAs Typical unattended operation period: 72 h No redundant, safety-grade, active ECCS and containment cooling systems no redundant emergency power supplies The ambient air is most often the ultimate heat sink no safetygrade service water system

5 5 Passive LWRs for near-term deployment Replacement of highly redundant safety-grade ECCS systems by passive systems does not necessarily improve safety but has the potential of significantly reducing capital and operating costs: reducing upstream complexity : Fuel, air, Diesel Electricity ECCS coolant delivery Startup and control

6 6 Avoid the sophisticated, redundant, etc. safety grade ECCS and its upstream complexity DG Room Ventilation System Emergency Bus Loading Program Initiation Signal Crankcase Ventilation Engine Governing Control DG Lubrication Oil System DC Pwr Courtesy of B. Shiralkar, GE Nuclear Energy Starting Air Diesel Generator Room 1 of 3 DG Cooling Water System Diesel DG Fuel Oil System DG Fuel Oil Storage and Transfer System Air Intake & Exhaust Plant Service Water Generator Control and Protection Generator Emergency Bus Breaker Closes < 10 s Breaker Breaker Breaker HVAC Plant Service Water Pump Motor HVAC Reactor Component Cooling Water Pump Motor RCCW HVAC Emergency Core Cooling System Pump Motor Typical of HPCS, LPCS, & RHR Water Source Conventional Active Plant Loads Loads Plant Service Water A Q Q ADS Logic DC Pwr M ECCS Logic Initiation Signal RPV Core ADS A S/P Aux. Water Source M Passive Plant

7 7 Key ES features Design Objectives Improve safety and simplify with passive systems Better plant economics Continued technical advancements Product Outcomes Auto safety response, no AC power or operator action required for at least 72 hrs No core uncovery in Design Basis Accidents Lower Core Damage Frequency ( ) Significant simplification lowers costs Evolutionary development Key Improvements: simplification Reduction in systems and equipment Reduction in operator challenges Reduction in core damage frequency (10x) Reduction in cost/mwe Tall chimney above core Flattened core

8 8 Optimized parameters for ES Parameter /4-Mk I (Browns Ferry 3) /6-Mk III (Grand Gulf) A ES Power (MWt/MWe) 3293/ / / /1550 Vessel height/dia. (m) 21.9/ / /7.1.7/7.1 Fuel Bundles (number) Active Fuel Height (m) Power density (kw/l) Recirculation pumps 2(large) 2(large) 10 zero Number of CRDs/type 185/LP 193/LP 205/FM 269/FM Safety system pumps zero Safety diesel generator zero Core damage freq./yr 1E-5 1E-6 1E-7 3E-8 Safety Bldg Vol (m 3 /MWe) <130

9 9 Cooling of the core under all conditions Primary intact: heat removal from the RPV 2 Primary breached: heat removal from the containment Heat removal by the turbine 1 Heat generation in the core

10 10 Passive systems for decay heat removal The classical ECCS and containment cooling systems replaced by: Natural-circulation cooling of the core (when the primary system is intact) Gravity Driven Cooling Systems (GDCS) (with the primary system breached) Passive Containment Cooling Systems (PCCS)

11 11 Primary system intact: ES isolation condenser Isolation Condenser (IC) directly connected to the RPV, immersed in pool outside the containment condenses steam from the core Courtesy of B. Shiralkar, GE Nuclear Energy

12 12 Decay heat removal: Breached primary system at high or medium pressure AP600, AP1000: Core Make-up Tank (CMT) SWR-1000: Emergency condenser immersed in core-flooding pool and permanently connected to the RPV For intermediate pressure levels in PWRs: injection of water from accumulators (~50 bar) or core reflood tanks (CRT ~15 bar) ES solution: automatic depressurization of the primary system and actuation of the Gravity-Driven Cooling System

13 13 ES Gravity Driven Cooling System (GDCS) Courtesy of B. Shiralkar, GE Nuclear Energy Following depressurization of the primary system by the ADS gravity driven flow keeps core covered

14 14 Main Steam Line break

15 15 Small pipe break at bottom of RPV

16 16 The alternative SWR-1000: Primary system breached: passive core cooling system Collapse of the voids in and above the core region leads to automatic activation of the Emergency Condenser connected to the RPV without valves and immersed in the Core Flooding Pool. 2-step cooling Loop seal: hot water does not rise and start boiling Needs some p in primary system

17 17 Decay heat removal from the Containment All containment systems profit from the passive heat sink provided by the containment structures and walls. These are needed to absorb the higher level of initial decay heat generation and the blowdown heat load. When the containment heat sink gets saturated, the decay heat level is lower Important timing considerations: heat capacity of system vs time at which cooling function is taken over Water pools used as heat sinks can boil off either to the atmosphere (1-step process) or to the containment (2-step process)

18 18 PCCS Passive Containment Cooling System Long term operation The DW pressure acts on the water level in the WW weir and opens the horizontal vents: the steam condenses in the pressure suppression pool The DW pressure also pushes the steam into the PCCS condensers and the noncondensables to be vented to the suppression pool: the preferred path for long-term decay heat evacuation A delicate pressure balance to ensure that decay heat goes to the PCCS pools

19 19 PCC Behavior in presence of steam/air mixtures The PANDA tests showed: PCC heat removal capacity is adjusted to actual requirements Decrease in decay heat and PCC-pool level are compensated by changing air content in PCC lower region Pool Height (m) Water level at test start active tube length Water level inactive primary side (air) Inactive secundary side (Water level low) Condenser Behavior of passive condensers in presence of steam/air mixtures is well understood Time (hours) Active condenser area is automatically adjusted to match requirements by adjustment of the air content in the lower part of the tubes

20 20 Summary: Passive core and containment cooling of the ES The Isolation Condensers (IC) condense steam from the RPV. The Gravity Driven Cooling System (GDCS) pool floods the core after depressurization of the primary system. The Passive Containment Cooling System (PCCS) condenses containment steam and vents the non-condensibles to the Suppression Pool. The PCCS system is modular and can be scaled to any power level

21 21 Passive containment cooling: PCCS The ES and the SWR-1000

22 22 ES Passive safety systems within Containment envelope Decay Heat HX s Above Drywell High Elevation Gravity Drain Pools All Pipes/Valves Inside Containment Raised Suppression Pool Courtesy of B. Shiralkar, GE Nuclear Energy

23 23 ES passive safety systems The ICS condenses steam from the RPV The GDCS floods the core after depressurization of the primary system The PCCS condenses containment steam and vents the noncondensibles to the Suppression Pool The PCCS system is modular and can be scaled to any power level; pools easy to refill ADS system Passive boron injection Non-safety-grade Diesels and closed Cooling Water and Service Water Systems

24 24 Natural Circulation The Dodewaard natural-circulation Natural circulation is not new Small, 183 MWth

25 25 Enhanced natural circulation in the ES Average Power per Bundle (MWt) A 6 A LUNGMEN CLINTON ESBW R ES a N Power Flow XLS Chart1 (5) Average Flow per Bundle (kg/s) Courtesy of B. Shiralkar, GE Nuclear Energy Higher driving head Chimney/taller vessel Reduced flow resistance Shorter core Increased downcomer flow area

26 26 Natural circulation in the ES Reduction in components pumps, controls, power supplies vessel internals Passive safety/natural circulation more water in the vessel no external piping, no canned motor penetrations Very good performance and reliability power/flow ratio similar to pumped plant large margin to combined t/h neutronic stability Load following with Control Rods

27 Much more water above the core Top of Active Fuel, TAF